The present disclosure relates generally to automobile steering systems and, more particularly, to a method and system for providing secondary vehicle directional control through the application of controlled braking applied to one or more wheels of the vehicle.
Traditionally, steering systems and braking systems for motor vehicles have each relied on the independent actuation of groups of components within the motor vehicle. Each component group actuated typically has a single function by which control of the motor vehicle is maintained. For example, with respect to steering systems, at least the front steerable wheels have been traditionally mechanically linked together and are synchronously steerable. In systems utilizing four-wheel steering, the front wheels are typically mechanically linked to each other and are synchronously steerable. The back wheels, although they are in electronic communication with the front wheels and provide an angle of steering relative to the front wheels, are likewise mechanically linked to each other and are synchronously steerable.
In the electronic braking systems currently utilized, the electronics evoke a response from hydraulic systems that apply the braking action to the wheels of the motor vehicle. During normal braking with an electronic braking system, a system computer interprets an operator input (i.e., the driver stepping on the brake pedal), and a signal is transmitted to mechanical actuators to apply the brakes. With regard to the typical vehicle configuration, the braking traditionally remains independent of the steering and the steering traditionally remains independent of the braking. When the motor vehicle experiences either function, the other remains the responsibility of the operator.
In the event of a steering system failure of a conventional steering system (short of a failure of a mechanical connection), the driver still has a measure of control over the steering. On the other hand, in a system such a xe2x80x9csteer-by-wirexe2x80x9d system, a failure may result in the driver losing directional control over the vehicle. While a secondary or backup steering system with redundant components and/or circuitry could be implemented to address such a possibility, the costs associated therewith dictate a less expensive, reliable alternative for a backup system to provide emergency directional control.
The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a method for implementing directional control of a motor vehicle. In an exemplary embodiment, the method includes determining whether a failure of a primary steering system of the motor vehicle exists. If a failure of the primary steering system exists, then a yaw moment is created on the vehicle by causing a differential longitudinal force to be applied with respect to a first wheel on one side of the vehicle and a second wheel on an opposite side of the vehicle, thereby causing the vehicle to turn in a commanded direction. The differential longitudinal force is created by applying a braking force to at least one of the first and second wheels of the vehicle.
In one embodiment, creating a yaw moment on the vehicle includes determining a desired directional response, determining whether a desired braking operation exists, and generating a brake torque output signal. Based upon the desired directional response and whether the desired braking operation exists, the brake torque output signal is used in selectively applying a braking force to at least one of the wheels of the vehicle.
Preferably, a switching mechanism is configured for selectively switching between a first, a second and a third mode of operation. The first mode of operation corresponds to an operational status of the primary steering system. The second mode of operation corresponding to a failure of the primary steering system with a commanded directional control operation of the motor vehicle. The third mode of operation corresponds to a failure of the primary steering system with a combined directional control operation and braking operation of the motor vehicle. The brake torque output signal is dependent upon which of the first, second and third modes of operation is selected by the switching mechanism.
In another embodiment, a steer-by-brake system for a motor vehicle includes a failed steering brake controller in communication with a braking system of the motor vehicle. The failed steering brake controller has a steering wheel angle as a first input thereto, a vehicle speed as a second input thereto, a vehicle yaw rate as a third input thereto, and a brake torque signal as an output therefrom. The brake torque output signal is used to selectively apply a braking force to at least one wheel of the motor vehicle when a failure of a primary steering system of the motor vehicle is detected, thereby creating a yaw moment on the motor vehicle so as to cause a turn in a commanded direction.